1. Field of the Invention
The present invention relates to a golf club head and, more particularly, to score lines on the face.
2. Description of the Related Art
Generally, on the face of a golf club head, a plurality of straight grooves are formed parallel to each other in the toe-and-heel direction. These grooves are called score lines, marking lines, face lines, or the like (to be referred to as score lines in this specification). These score lines have an effect of increasing the back spin amount of a shot or suppressing a significant decrease in the back spin amount of a shot in case of a rainy day or a shot from the rough. For this reason, various shapes of a score line are proposed. For example, in the specification of the U.S. Pat. No. 6,733,400, there is disclosed an iron golf club set in which the heads of respective golf clubs include score lines each having a protrusion at its bottom portion, so as to adjust the back spin amount for each club number.
Factors of a score line which particularly influence the backspin amount are the edge angle of a score line, the depth of a score line, and the like. The smaller the edge angle of a score line, the higher the backspin amount. The larger the depth of a score line, the higher the backspin amount in case of a rainy day or a shot from rough.
However, according to the rule about the score lines of a golf club head for competitions, a cross-sectional area A (inch2) of a score line, a width W (inch) of the score line measured based on the 30 degrees measurement method, and a distance S (inch) between the score lines adjacent to one another must satisfy A/(W+S)≦0.003 (to be referred to as the area rule, hereinafter). When the edge angle of the score line is decreased or the depth of the score line is increased, the cross-sectional area of the score line increases, and therefore it may not conform to the area rule. On the contrary, when the score lines are formed to conform to the area rule, a sufficient backspin amount may not be obtained.